The present invention relates to the fabrication of integrated circuits. More particularly, the invention provides a technique, including a method and an apparatus, for increasing the deposition rate of dielectric films, at a given temperature, while demonstrating good gap filling properties comparable with existing film deposition techniques.
Deposition of dielectric films, such as silicon dioxide (SiO.sub.2), silicon nitride (SiN), silicon oxynitride (SiON) and the like, over a semiconductor substrate is a common step in the formation of some integrated circuit (IC) structures. For example, dielectric films may be used to form gates of field effect transistors (FETs), spacers separating adjacent FETs, or sacrificial layers in the formation of dynamic random access memories. These films are typically deposited employing chemical vapor deposition (CVD) techniques.
Particularly suitable as an inter-level dielectric, SiO.sub.2 films may be formed by using silane, SiH.sub.4, as a silicon source and molecular oxygen, O.sub.2, as an oxygen source, forming on a substrate according to the following reaction: EQU SiH.sub.4 +O.sub.2.fwdarw.SiO.sub.2 (1)
Historically, silane has provided adequate silicon dioxide inter-level dielectric films at varying chamber pressures and substrate temperatures. However, advances in integrated circuit technology have led to a scaling down of device dimensions and an increase in chip size and complexity. This has necessitated improved methods for deposition of dielectric films with enhanced gap filling properties. As a result, tetraethylorthosilicate, Si(OC.sub.2 H.sub.5).sub.4, [hereinafter referred to as TEOS] as a silicon source has gained wide acceptance due to its superior gap-filling properties.
TEOS reacts with molecular oxygen, O.sub.2, as an oxygen source to form SiO.sub.2 on a substrate according to the following reaction: EQU Si(OC.sub.2 H.sub.5).sub.4 +O.sub.2.fwdarw.SiO.sub.2 +by products (2)
Originally, TEOS had limited use as an inter-level dielectric film, because of the high substrate temperature required to deposit the same efficiently. Reaction (2) required a temperature of approximately 700.degree. C. in order to achieve an acceptable deposition rate. The aforementioned temperature is incompatible with aluminum metallization. As a result, there has been a constant endeavor to lower the deposition temperature of inter-level dielectric films formed using TEOS as a silicon source.
One employs a plasma in the chamber for plasma enhanced chemical vapor deposition (PECVD) apparatus. Another such effort replaces molecular oxygen with ozone, O.sub.3, to produce a silicon dioxide film according to the following reaction: EQU Si(OC.sub.2 H.sub.5).sub.4 +O.sub.3.fwdarw.SiO.sub.2 +by-products (3)
With this reaction, silicon dioxide films may be deposited at temperatures as low as 400.degree. C. while still providing an acceptable deposition rate.
Another composition of dielectric films employs nitrogen sources to form silicon nitride films on a substrate. The silicon nitride films are amorphous insulating materials that are typically used as a final passivation layer for integrated circuits, as a mask for selective oxidation of silicon, and as a gate dielectric material for MNOS devices.
An early composition of a silicon nitride film, Si.sub.3 N.sub.4 is deposited using low pressure chemical vapor deposition (LPCVD) techniques according to the following reaction: EQU SiH.sub.2 Cl.sub.2 +NH.sub.3.fwdarw.Si.sub.3 N.sub.4 (4)
Similar to reaction (2), reaction (4) had limited use, because of the high substrate temperature required to deposit the same efficiently. In order to achieve an acceptable deposition rate, reaction (4) requires a temperature of approximately 800.degree. C., which is incompatible with many post deposition processes. To further reduce the deposition temperature of silicon nitride films, the following PECVD reactions has been developed: EQU SiH.sub.4 +NH.sub.3 +N.sub.2.fwdarw.SiN(H) (5) EQU SiH.sub.4 +NH.sub.3 +N.sub.2 O.fwdarw.SiON (6)
Both reactions (5) and (6) may be deposited at a process temperature as low as 200.degree. C. while still providing an acceptable deposition rate.
What is needed, therefore, is a technique for improving the deposition rate of dielectric films without increasing the deposition temperature of the same.